Numerous applications necessitate the metered injection of two different liquids into a reaction chamber, in which the two liquids are allowed to react with one another. Such an application is a so-called reformer for a fuel cell, in which hydrogen and oxygen are essentially allowed to react to form water in a xe2x80x9ccold combustion,xe2x80x9d thereby generating electrical energy.
The use of these fuel cells as an alternative for internal-combustion engines stipulates that sufficient quantities of hydrogen also be conveyed, in gaseous or cryogenic form, in a storage vessel. This requires a large structural space and high weight, and also represents a considerable potential danger.
It is therefore desirable to produce the hydrogen using a catalytic reformer immediately before the conversion in a fuel cell from other fuels, such as automobile fuel, diesel fuel or methanol. In a reformer of this type, the injected fuel reacts with additionally injected water to form carbon dioxide and hydrogen, which can then be converted into electrical energy in a known manner in the fuel cell.
Regarding fuel cells, DE 196 23 937 C1 and DE 199 18 997 A disclose mixing the two liquids in liquid or vapor form in the necessary ratio in advance, then supplying the mixture to the reactor or reformer. In DE 196 23 937 C1, varying load requirements are compensated through the maintenance of an ideal value for the mixture in a mixture-preparation stage; afterward, the supply of the two liquids is controlled. Adaptation to different load requirements is effected through the controlled extraction of the mixture from the mixture-preparation stage.
It is the object of the invention to create an injection device that allows two liquidsxe2x80x94in the case of the fuel cell, fuel and waterxe2x80x94to be metered directly into a reaction chamber via a common nozzle. Here, both the total quantity and the quantity ratio of the two liquids relative to one another are to be varied as a function of different operating points and/or changing load requirements.
In accordance with the invention, this object is accomplished by an injection device for the metered injection of two liquids, in predeterminable quantity ratios, into a reaction chamber, the device having a housing that includes an injection nozzle, the opening of which forms an injection valve with the valve seat in the housing and a valve body that can be positioned on the valve seat; the valve body can be moved by a first actuator; the collection chamber of the device is associated with the nozzle opening, and is connected to a supply line for the first liquid and a supply line for the second liquid, with a metering valve being set up to block at least one supply line to the collection chamber, the valve being actuated by a second actuator; one of the two liquids is under a higher pressure than the other liquid; the device further has a control device, which is connected to the two actuators and can actuate the two actuators as a function of a load-stipulated total injection quantity and as a function of a predeterminable quantity ratio of the two liquids, with at least one valve being actuated in a clocked manner. An injection device of this type allows the two liquids to be stored in the collection chamber of the injection device prior to the opening of the injection valve. Because a separate metering valve is provided for one of the liquids, preferably the liquid subjected to higher pressure, it is possible to introduce a predeterminable quantity of this liquid into the collection chamber of the injection device. If the nozzle opening is opened in the actuation of the injection valve, the pre-stored quantity of the one liquid is entrained by the incoming quantity of the other liquid. Thus, the total injection quantity can be injected directly into the reaction chamber as the two liquid components are mixed. The duration of the opening time of the injection valve determines the incoming quantity of the other liquid, preferably the liquid subjected to a lower pressure, both with respect to the partial quantity required for the reaction and the total injection quantity.
The arrangement of an additional metering valve that can be actuated independently of the injection valve, and in a clocked manner, offers numerous options for setting the total quantity of injected liquid, as well as for setting the quantity ratio of the two liquids to be injected. It is possible to establish different mixture ratios between these two liquids and the total quantity to be injected, not only due to the displacement of liquid out of the collection chamber during the opening time of the metering valve for the liquid under high pressure, the displacement allowing a matching quantity of liquid to be stored in advance in the collection chamber, but also through a temporary, overlapping opening of the metering valve with respect to the injection valve, or through an intermittent or clocked opening of the metering valve while the injection valve is open.
It is especially advantageous to position the discharge of the supply line for the liquid under the higher pressure near the valve seat of the valve body of the injection valve. In this case, when the liquid under the higher pressure is introduced into the collection chamber, the other liquid can be xe2x80x9cpressed backxe2x80x9d into its pressure chamber. Because the quantity of liquid stored in the collection chamber is under the pressure of the other liquid after the metering valve has been closed, when the injection valve is open and the metering valve is closed, the stored liquid is injected into the reaction chamber, followed after a slight delay by the other liquid, which guarantees a successful reaction.
In a further embodiment of the invention, it is provided that the actuators are electromagnetic, with the movable valve bodies of the injection valve and the metering valve respectively being connected to an armature and a restoring spring that acts in the closing direction. Such actuators can be controlled with high precision with respect to the opening period by a corresponding control device, so, following an appropriate calibration, an injection device is available that permits a very precise, as-needed actuation of the metering valve and/or the injection valve when the liquids are supplied to the injection device under preset pressures.
Further features and embodiments of the invention ensue from the claims.